Mobile phones, personal digital assistants (“PDAs”), digital cameras, MP3 players, and other portable electronic devices utilize SSL devices (e.g., LEDs) for background illumination. SSL devices are also used for signage, indoor lighting, outdoor lighting, and other types of general illumination. FIG. 1A is a cross-sectional view of a conventional SSL device 10 with lateral contacts. As shown in FIG. 1A, the SSL device 10 includes a substrate 12 carrying an LED structure 11 having N-type gallium nitride (GaN) 14, GaN/indium gallium nitride (InGaN) multiple quantum wells (“MQWs”) 16, and P-type GaN 18. The SSL device 10 also includes a first contact 20 on the P-type GaN 18 and a second contact 22 on the N-type GaN 14. The first contact 20 typically includes a transparent and conductive material (e.g., indium tin oxide (“ITO”)) to allow light to escape from the LED structure 11. FIG. 1B is a cross-sectional view of another conventional LED device 10′ in which the first and second contacts 20 and 22 are opposite of each other. In the LED device 10′, the first contact 20 typically includes a reflective and conductive material (e.g., aluminum or silver) to direct light toward the N-type GaN 14.
As discussed in more detail below, it has been observed that materials with good transparent or reflective properties often do not form satisfactory Ohmic contacts with components of the SSL structure 11, and vice versa. For example, the SSL device 10 having ITO in contact with the P-type GaN 18 may have undesirable high series resistance. In another example, silver processed to maintain its reflectivity may form a Schottky barrier with the P-type GaN 18. The high series resistance and/or Schottky barrier may result in parasitic electrical impedance during operation and/or otherwise degrade the electrical performance of the LED devices. In yet another example, if silver is annealed at high temperatures to form good electrical contact with the SSL structure 11, its reflectivity may degrade. Accordingly, it would be desirable to mitigate the impact of electrical contact resistance in SSL devices.